Spray coating apparatus

ABSTRACT

A spray coating apparatus includes a spray gun which contains a piston pump operated by the pressure responsive fluid actuator having a hollow, flexible, thin-walled shell defining a pneumatic fluid chamber of variable volume for pressurizing fluent material delivered to the gun nozzle. A control circuit operates a nozzle valve in timed relation to the operation of the pump to intermittently release streams of coherent fluent material through the nozzle.

United States Patent 11 1 1111 3,844,483

Gray Oct. 29, 1974 SPRAY COATING APPARATUS Prima Examiner-M. Henson Wood Jr. h ry [75] lnve mOr J" n C Gray Harvard Mass Assistant ExaminerM1chael Y. Mar Asslgneer Trish Energetics, Harvard, Attorney, Agent, or Firm-McCormick, Paulding &

MaSS- Huber [22] Filed: June 14, 1973 211 Appl. No.: 369,947 [57] ABSTRACT A spray coating apparatus includes a spray gun wh1ch contains a piston pump operated by the pressure re- [52] U.S. Cl. 239/322, 417/404 sponsive fluid actuator having a hollow flexible, thin [51] Int. Cl BOSb 1/32 walled Shell defining a pneumatic fluid chamber of [58] Field Of Search 239/302, 322, 321; variable volume for preSSul-izing fluent i l li 417/384, 368, 394, 404; 9 ered to the gun nozzle. A control circuit operates a nozzle valve in timed relation to the operation of the [5 6] References Clted pump to intermittently release streams of coherent flu- UNITED STATES PATENTS ent material through the nozzle.

2,l53,5l9 4/1939 Horton 239/322 X 3,700,359 10/1972 Vanderjagt .1 417/404 20 Clams 4 Drawmg F'gures 1 SPRAY COATING APPARATUS BACKGROUND or THE INVENTION BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing and initially to FIG. 1,

This invention relates to spray coating apparatus and 5 a spray coating apparatus embodying the present indeals more particularly with an improved automatic apparatus which includes a spray gun of so-called airless type which emits coherent fluent material under pressure through a nozzle.

The apparatus of the present invention may be useful for many coating purposes, however, it has proven particularly suitable for applying liquid abrasive compound to buffing and polishing wheels and the like. Such wheels generally run at speeds in the range of 600 1,750 revolutions per minute to provide surface speeds which may range from 5,000 to 6,000 feet per minute. When a spray gun of the so-called air atomizing type is employed to apply liquid abrasive compound to a wheel of the aforedescribed kind considerable overspray may and usually does result from atomization of the abrasive compound and failure of the compound spray to penetrate windage generated by the wheel. The aforesaid overspray condition usually results in substantial compound loss accompanied by housekeeping problems and possible fire hazards, all of which add substantially to operational cost.

Heretofore, various airless spray apparatus has been provided to overcome the aforesaid problems, however, such apparatus usually requires relatively expensive pumping mechanism and is generally expensive to install and maintain. Accordingly, it is the general aim of the present invention to provide an improved airless spray apparatus particularly suitable for such difficult installations where emission of coherent fluent material at relatively high pressure is desired.

The apparatus of the present invention includes a spray gun which has a self-contained pneumatically operated pumping mechanism for pressurizing fluent material within the gun prior to discharge through the gun nozzle. The simple durable construction of the gun and associated control mechanism which comprise the apparatus assures relatively trouble free service and facilitates manufacture at low cost.

SUMMARY OF THE INVENTION In accordance with the present invention, an improved airless spray apparatus is provided which comprises a spray gun having a self-contained pump operated by a pneumatic fluid pressure responsive actuator to deliver'fluent material under pressure to a spray nozzle. A nozzle valve operates in timed relation with the pump to emit a stream of coherent fluent material from the nozzle each time the pump operates. The material; is or may be atomized through interaction with atmospheric air as it is emitted from the nozzle.

BRIEF DESCRIPTION OF THE DRAWING vention includes a spray gun indicated generally by the reference numeral 10 and associated control mechanism. The gun 10 is of the so-called airless" type and emits coherent fluent material in a stream from a nozzle. In this regard, the spray gun of the present invention may be readily distinguished from spray guns of the so-called air atomizing type in which both fluent material and air under pressure are simultaneously emitted from a nozzle, the material being substantially entrained in an air stream as it leaves the spray nozzle.

The illustrated gun 10 has a pump indicated generally at 12 and an associated nozzle assembly designated generally by the numeral 14 which receives fluent material under pressure from the pump and discharges it at a point of emission 16. The nozzle assembly 14 includes a nozzle valve indicated generally at 18 and movable between open and closed positions relative to the point of emission 16 to control discharge of material therefrom. Fluent material fed into the gun through a supply line 20, which communicates with a source of material under pressure (not shown in FIG. 1), flows past a check valve 22 associated with the supply line 20 and into the pump 12. The pump is operated by a pneumatic fluid pressure responsive actuator 24, which converts fluid energy input to mechanical output, and delivers material to the nozzle assembly under pressure. A pneumatic control circuit indicated generally by the numeral 25 in FIG. 4, and hereinafter further described, controls operation of the fluid actuator 24 and also operates the nozzle valve 18 in timed relation to the operation of the actuator to intermittently emit or eject streams of coherent fluent material at the point of emission 16.

The gun 10 includes a gun body indicated generally by the numeral 26 which contains the pump 12 and supports the nozzle assembly 14. A housing mounted in fixed position to the rear end of the body and designated generally at 28 provides support and protective enclosure for the fluid actuator 24. Preferably and as shown the housing 28 also includes a fluid pressure accumulator indicated generally at 30 which has a pressure chamber 31 and comprises a part of the control mechanism or pneumatic fluid control circuit 25.

Considering now the structure of the gun 10 in further detail, the body 26 is generally cylindrical and has an integral mounting bracket which depends therefrom to facilitate mounting the gun in fixed position on a horizontal rod or the like, such as indicated at 29. A stepped bore 32 extends coaxially through the body and contains a radially disposed washer 33 and an associated cylindrical sleeve 34 which cooperate to define a cylindrical chamber 36 of the pump 12. The pump further includes a piston 38 supported in the chamber 36. for sliding movement in one and an opposite direction therein to vary the volume of the chamber. Front and rear piston rods respectively indicated at 40 and 42, threaded into the piston 38, extend in opposite directions therefrom and coaxially through the bore 32. The front piston rod 40 is supported at its forward end by a bushing 44 carried by a generally cylindrical retainer 46 boltedto the forward end of the body 26. The

retainer provides a closure for the forward end of the bore 32 and also serves to retain the washer 33 and sleeve 34 in fixed position therein. A retaining washer 47 received on the forward end of the rod and retained thereon by a snap-ring is accessible through an opening in the forward end of the retainer 46 and cooperates with the retainer to limit rearward travel of the piston 38 relative to the pump chamber 36. A snap-in cover 50 provides a closure for the opening in the forward end of the retainer. The rear piston rod 42 extends rearwardly from the piston 38 and is supported by a bushing 48 received in the rear end portion of the bore 32 and retained therein by a snap-ring. The rear end portion of the rod 42 is externally threaded to facilitate connection to the actuator 24, as will be hereinafter further discussed. An exhaust port 54 which contains a suitable filter media opens through one side of the body 26 and communicates with the forward end of the pump chamber 36, substantially as shown.

Fluent material is fed into the pump chamber 36 through a pipe fitting S6 threaded into the body 26 and cooperating with the supply line 20 to define a fluid inlet passageway 58 which communicates with the rear end of the pump chamber. The check valve 22 comprises a generally conventional ball check valve mounted within the passageway 58 and arranged to permit material to flow from a supply source or reservoir indicated at 59 in FIG. 4 through the line 20 and the passageway 58 and into the pump chamber, however, the check valve 22 prevents retrograde flow of material from the pump chamber to the supply source.

The nozzle assembly is mounted on the body 26 by a threaded pipe coupling 60 which defines a fluid outlet passageway 62 in communication with the rear end of the pump chamber 36 and the nozzle assembly 14. The latter assembly includes a cylindrical nozzle body 64 which has a stepped bore 66 extending coaxially therethrough. A nozzle cap 68 threaded onto the forward end of the body 64 retains a nozzle 70 which defines the point of emission 16. The nozzle valve 18 comprises a carbide valve insert 72 retained in the forward end of the bore 66 and an axially elongated needle valve 74 supported for axial movement in the bore 66 between open and closed positions relative to the insert 72. The needle valve 72 has a carbide tip at its forward end for seating engagement with a rearwardly facing seating surface on the insert 72 in closed position to prevent discharge of material from the nozzle 70. Movement of the needle valve 74 rearwardly relative to the body exposes a passageway in the insert 72 to permit material to flow from the bore 66 through the latter passageway to and through the point of emission 16. A piston 76 attached to the rear end of the needle valve 74 is slidably received in a piston chamber 78 defined by a cylindrical valve body 80 threadably attached to the rear of the nozzle body 64. The needle valve 74 is biased to its closed position by a compression spring 82 received within the piston chamber and acting between the piston 76 and a vented end cap 84 retained in the rear end of the valve body 80 by a snap-ring. A pneumatic fluid pressure inlet line 86 associated with the pneumatic control circuit shown in FIG. 4, and hereinafter further described, communicates with the piston chamber 78 forwardly of the piston 76.

As previously noted, the housing 28 is fastened to the rear gun body 26. In more particularity, the housing comprises a generally circular housing mounting plate 88 and a tubular sleeve 90 secured to the plate and extending rearwardly therefrom. A generally cylindrical accumulator valve body 92, which contains valves and fluid ports hereinafter further discussed, is disposed within the sleeve 90 intermediate the ends thereof and sealed thereto by an O-ring 93. The valve body 92 cooperates with the mounting plate 88 and a portion of the sleeve 90 to define a compartment 94 for receiving the actuator 24. An accumulator end cap 96 fastened in fluid tight engagement with the rear end of the sleeve 90, substantially as shown, cooperates with the accumulator valve body 92 and a rear portion of the sleeve 90 to define the accumulator 30 which includes the fluid pressure chamber 31.

The pressure responsive pneumatic fluid pressure actuator 24 is supported in the compartment 94 and may take various forms, but preferably, and as shown, it comprises an axially elongated thin-walled shell 98 which defines a pressure chamber 100 of variable volume. The shell 98 has coaxially aligned coupling members 102 and 104 secured to opposite ends thereof, the coupling member 102 being threaded onto the rear end of the rear piston rod 42. The other coupling member 104 has a fluid inlet opening therethrough which communicates with the actuator chamber 100. A pipe nipple or the like such as indicated at 106 threadably secured to the valve body 92 and threaded into the inlet opening in the coupling 104 retains the coupling 104 in fixed position relative to the gun body 26 and provides a portion of a fluid or air passageway 108 which communicates with the actuator chamber 100 and with air passageways formed in the valve body 92 and hereinafter more fully described.

The shell 98 is adapted for radial expansion and axial contraction in response to changes in pressure in the chamber 100, axially extended and contracted positions of the shell 98 being respectively indicated in full and broken lines in FIG. 1. The shell 98 is preferably formed from an elastomeric material suitably reinforced so that the surface area thereof remains substantially constant in both its axially extended and contracted positions, thus, when the actuator is operated substantially all fluid energy input is available for moving the coupling member 102 and its associated piston rod 42 toward the coupling member 104 and little or no fluid energy is expended in stretching the shell material.

In its axially contracted position or inflated condition, the actuator 24 is characterized by a generally prolate speriodal configuration, as it appears in full lines in FIG. 1. When the actuator is in its axially extended position, however, the shell 98 has a generally convoluted cross-sectional configuration characterized by a plurality of circumaxially spaced ridges and valleys as shown in FIG. 2, wherein the extended position of the actuator 24 is indicated in broken lines. The illustrated actuator 24 is an AMPFLEX manufactured by Trish Energetics Inc., Harvard, Massachusetts. Reference may be had to US. Pat. No. 3,645,173 to Yarlott, issued Feb. 29, i972 for FLUID ACTUATOR for more complete description of the actuator 24.

The accumulator 30 is adapted to contain a charge of pneumatic fluid or pressurized air sufficient to effect at least one operation of the actuator 24 and has an air inlet passageway 110 formed in the valve body 92 as best shown in FIGS. 3 and 4, which communicates with the accumulator chamber 31 and with a pneumatic fluid pressure source 112, which contains a source of air under pressure at a presently preferred pressure of approximately 100 PSI. A normally open accumulator inlet valve 114 supported within the valve body 92 controls flow of pressure fluid from the pressure source 112 into the pressure chamber 31. The illustrated valve 114 is manufactured by Humphrey Products, Kalamazoo, Michigan, and is further identified as a Y-l Humphrey valve. The valve body 92 also has an air outlet passageway 116 which communicates with the accumulator pressure chamber 31 and with the actuator chamber 100 via the air passageway 108. An exhaust air passageway 118 is also formed in the valve body 92 to communicate with the air passageway 108 for exhausting air from the accumulator. The flow of pneumatic pressure fluid into and from the actuator 24 is controlled by an accumulator outlet valve 120 supported in the valve body 92. In the illustrated case a Y-25O Humphrey valve is used for this purpose.

Further considering the control circuit 25 and referring more particularly to FIG. 4, the control circuit preferably includes the accumulator and also a solenoid operated pilot valve 122 for controlling the accumulator inlet and outlet valves 114 and 120. Preferably, the circuit is also provided with an adjustable electrical timer 124 for operating the solenoid associated with the pilot valve to effect an automatic cycle of the gun 10.

The normally closed pilot valve is connected to the pneumatic fluid pressure source 112 by an air supply line 126 and, to the two accumulator valves by an air line 128, and to the nozzle valve 18 by the line 86.

In operation, fluent material which may, for example, comprise liquid abrasive compound or the like is fed into the gun from the supply source 59 and through the supply line 20 at a pressure preferably in the range of 50 to 60 psi. At the start of the operational cycle, the accumulator valves 114 and 120 and the pilot valve 122 are in the positions shown in FIG. 4. The accumulator 30 is connected to the pneumatic fluid pressure source 112 and contains a charge of pressure fluid sufficient to effect at least one operation of the actuator 24.

Operation of the solenoid in response to the timer 124 opens the normally closed pilot valve 122 whereby fluid pressure is substantially simultaneously supplied to the accumulator inlet and outlet valves 114 and 120 to change the position of the latter valves. The normally open accumulator inlet valve 114 closes to prevent further pressure fluid from entering the accumulator from the source 112. The normally closed accumulator outlet valve 120 opens to connect the actuator to the accumulator 30 and to block the exhaust passageway 118. Thus, the charge from the accumulator 30 is dumped into the actuator 24 causing it to expand radially and contract axially to move the piston 38 rear-, wardly. The latter movement of the piston applies pressure to the material in the pump chamber 36, the associated inlet and outlet passages 58 and 62, and in the body of the nozzle assembly 14. It will be noted that the operation of the nozzle valve 18 is also controlled by the pilot valve 122, however, the pneumatic control circuit 25 is constructed and arranged to operate the nozzle valve 18 in timed relation with the operation of the actuator 24. This timed relationship is attained by making the air line 86 which supplies pressurized air to the nozzle valve somewhat longer than the air supply 128 which supplies the air to operate the accumulator valves 114 and 120. Thus, the accumulator valves operate and, in turn, operate the actuator 24 before the nozzle valve 18 is operated or moved to its open position. Thus, the material in the gun 10 is pressurized by the pump 12 before the nozzle valve 18 opens to emit the pressurized material at the point of emission 16.

When the timer 124 shuts off, the pilot valve 122 closes and the accumulator valves 114 and reverse position and return to the positions shown in FIG. 4. The nozzle valve 18 is closed by the spring 82. The material which enters the gun under pressure from the supply line 20 acts upon the rear face of the piston to return the piston to its forward position and return the actuator 24 to its axially extended position in preparation for the next timed cycle. Preferably, the nozzle valve is arranged to open after the start of the pump stroke and to close before completion of the pump stroke.

I claim:

1. A spray coating apparatus comprising a pump assembly including means defining a pump chamber and a pump piston supported in said chamber for movement in one and an opposite direction therein to vary the volume of said pump chamber, a nozzle assembly including a nozzle defining a point of emission for a stream of coherent fluent material, a nozzle valve movable between open and closed positions relative to said nozzle, said nozzle valve in said open position permitting discharge of fluent material from said point of emission and in said closed position preventing discharge of material therefrom, means defining an inlet passageway communicating with said pump assembly for connection to a source of fluent material to provide a material flow path from the source to said pump chamber, a check valve associated with said inlet passageway for permitting material to flow from the source to said pump chamber and preventing retrograde flow of material from said pump chamber to the source, means defining an outlet passageway communicating with said pump assembly and said nozzle assembly for providing a material flow path from said pump chamber to said point of emission, a pneumatic fluid pressure responsive actuator comprising a hollow flexible thin-walled shell defining a pneumatic chamber of variable volume and having generally axially opposed end portions, one of said end portions being secured in fixed position relative to said pump chamber defining means, the other of said end portions being attached to said pump piston, said end portions being movable generally toward and away from each other in response to variation of pneumatic fluid pressure in said pneumatic chamber, said actuator being operable to move said pump piston in one direction to reduce the volume of said pump chamber, and means for controlling the operation of said actuator.

2. A spray coating apparatus as set forth in claim 1 wherein said shell has a surface of substantially constant area in each of the positions of said actuator, said shell in said axially extended position of said actuator has a fluted configuration defined by a circumaxially spaced series of axially extending ridges and valleys, and said shell in said axially retracted position of said actuator has a generally prolate spheroidal configuration.

3. A spray coating apparatus as set forth in claim 2 wherein said shell is made from elastomeric material reinforced with other material to prevent change in the surface area thereof.

4. A spray coating apparatus as set forth in claim 1 wherein said pump piston is movable in said one direction in response to movement of said actuator from its axially extended toward its axially contracted position.

5. A spray coating apparatus as set forth in claim 1 wherein said apparatus includes means for operating said nozzle valve in timed relation to the operation of said actuator.

6. A spray coating apparatus as set forth in claim 5 wherein said means for controlling the operation of said actuator comprises said means for operating said nozzle valve in timed relation to the operation of said actuator.

7. A spray coating apparatus as set forth in claim 6 wherein said nozzle assembly includes means for biasing said nozzle valve to its closed position and pneumatically actuated means for moving said nozzle valve to its open position.

' 8. A spray coating apparatus as set forth in claim 1 wherein said means for controlling the operation of said actuator comprises a pneumatic pressure fluid control circuit including a fluid pressure accumulator for connection to a source of pneumatic pressure fluid for receiving and containing a charge of pneumatic pressure fluid sufficient to effect operation of said actuator and control valve means for controlling the flow of pressure fluid from the source into said accumulator and for controlling the flow of pressure fluid from said accumulator into said actuator to effect operation thereof.

9. A spray coating apparatus comprising a pump assembly including means defining a pump chamber and a pump piston supported in said chamber for movement in one and an opposite direction therein to vary the volume of said pump chamber, a nozzle assembly including a nozzle defining a point of emission for a stream of coherent fluent material, a nozzle valve movable between open and closed positions relative to said nozzle, means for biasing said nozzle valve to its closed position, and pneumatically actuated means for moving said nozzle valve to its open position, said nozzle valve in said open position permitting discharge of fluent material from said point of emission and in said closed position preventing discharge of material therefrom, means defining an inlet passageway communicating with said pump assembly for connection to a source of fluent material to provide a material flow path from the source to said pump chamber, a check valve associated with said inlet passageway for permitting material to flow from the source to said pump chamber and preventing retrograde flow of material from said pump chamber to the source, means defining an outlet passageway communicating with said pump assembly and said nozzle assembly for providing a material flow path from said pump chamber to said point of emission, a pneumatic fluid pressure responsive actuator operably connected to said pump piston for moving it in one direction to reduce the volume of said pump chamber, and means for controlling the operation of said actuator and for operating said nozzle valve in timed relation to the operation of said actuator.

10. A spray coating apparatus as set forth in claim 9 wherein said actuator comprises a hollow flexible thinwalled shell defining a pneumatic chamber of variable volume and having generally axially opposed end portions, said end portions being movable generally toward and away from each other between axially contracted and axially extended positions in response to variation of pneumatic fluid pressure in said chamber, one of said end portions being secured in fixed position relative to said pump chamber defining means, the other of said end portions being attached to said pump piston.

11. A spray coating apparatus as set forth in claim 10 wherein said shell has a surface of substantially constant area in each of the positions of said actuator, said shell in said axially extended position of said actuator has a fluted configuration defined by a circumaxially spaced series of axially extending ridges and valleys, and said shell in said axially retracted position of said actuator has a generally prolate spheroidal configuratron.

12. A spray coating apparatus as set forth in claim 9 wherein said means for controlling the operation of said actuator comprises a pneumatic control circuit which includes a pilot valve for connection to a source of pneumatic pressure fluid and movable between open and closed positions, a pneumatically operated control valve means for controlling the operation of said actuator, means defining a first pneumatic fluid passageway communicating with said pilot valve and said control valve means, means defining a second pneumatic fluid passageway communicating with said pilot valve and said pneumatically actuated means for moving said nozzle valve, and means for operating said pilot valve to simultaneously connect said first and second pneumatic fluid passageways to the pneumatic pressure fluid supply source.

13. A spray coating apparatus as set forth in claim 12 wherein said second pneumatic fluid passageway is substantially longer than said first pneumatic fluid passageway and comprises said means for operating said nozzle valve in timed relation to the operation of said actuator.

14. A spray coating apparatus as set forth in claim 13 wherein said means for operating said pilot valve comprises a solenoid and said apparatus includes an adjustable timer for operating said solenoid to control the operating cycle of said apparatus.

15. A spray coating apparatus comprising a pump assembly including means defining a pump chamber and a pump piston supported in said chamber for movement in one and an opposite direction therein to vary the volume of said pump chamber, a nozzle assembly including a nozzle defining a point of emission for a stream of coherent fluent material, a nozzle valve movable between open and closed positions relative to said nozzle, said nozzle valve in said open position permitting discharge of fluent material from said point of emission and in said closed position preventing discharge of material therefrom, means defining an inlet passageway communicating with said pump assembly for connection to a source of fluent material to provide a material flow path from the source to said pump chamber, a check valve associated with said inlet passageway for permitting material to flow from the source to said pump chamber and preventing retrograde flow of material from said pump chamber to the source,

means defining an outlet passageway communicating with said pump assembly and said nozzle assembly for providing a material flow path from said pump chamber to said point of emission, a pneumatic fluid pres sure responsive actuator operably connected to said pump piston for moving it in one direction to reduce the volume of said pump chamber, and a pneumatic pressure fluid control circuit for controlling the operation of said actuator and including a fluid pressure accumulator for connection to a source of pneumatic pressure fluid for receiving and containing a charge of pneumatic pressure fluid sufficient to effect operation of said actuator and control valve means for controlling the flow of pressure fluid from the source into said accumulator and for controlling the flow of pressure fluid from said accumulator into said actuator to efiect operation thereof.

16. A spray coating apparatus as set forth in claim wherein said actuator comprises a hollow flexible thinwalled shell defining a pneumatic chamber of variable volume and having generally axially opposed end portions, said end portions being movable generally toward and away from each other between axially contracted and axially extended positions in response to variation of pneumatic fluid pressure in said chamber, one of said end portions being secured in fixed position relative to said pump chamber defining means, the other of said end portions being attached to said pump piston.

17. A spray coating apparatus as set forth in claim 16 wherein said shell has a surface of substantially constant area in each of the positions of said actuator, said shell in said axially extended position of said actuator has a fluted configuration defined by a circumaxially spaced series of axially extending ridges and valleys, and said shell in said axially retracted position of said actuator has a generally prolate spheroidal configura tion.

18. A spray coating apparatus as: set forth in claim 15 wherein said fluid control circuit includes a pilot valve for operating said control valve means and means for operating said pilot valve.

19. A spray coating apparatus as set forth in claim 18 wherein said means for operating said pilot valve comprises an adjustable cycle timer.

20. A spray apparatus as set forth in claim 18 wherein said control valve means comprises a normal open first accumulator valve for controlling the flow of pressure fluid from the source into said accumulator and a normally closed second accumulator valve for controlling the flow of pressure fluid from said accumulator into said actuator, said first and second accumulator valves being operable substantially simultaneously in response to operation of said pilot valve to prevent flow of pressure fluid from the source into said accumulator and to permit flow of pressure fluid from said accumulator into said actuator. 

1. A spray coating apparatus comprising a pump assembly including means defining a pump chamber and a pump piston supported in said chamber for movement in one and an opposite direction therein to vary the volume of said pump chamber, a nozzle assembly including a nozzle defining a point of emission for a stream of coherent fluent material, a nozzle valve movable between open and closed positions relative to said nozzle, said nozzle valve in said open position permitting discharge of fluent material from said point of emission and in said closed position preventing discharge of material therefrom, means defining an inlet passageway communicating with said pump assembly for connection to a source of fluent material to provide a material flow path from the source to said pump chamber, a check valve associated with said inlet passageway for permitting material to flow from the source to said pump chamber and preventing retrograde flow of material from said pump chamber to the source, means defining an outlet passageway communicating witH said pump assembly and said nozzle assembly for providing a material flow path from said pump chamber to said point of emission, a pneumatic fluid pressure responsive actuator comprising a hollow flexible thin-walled shell defining a pneumatic chamber of variable volume and having generally axially opposed end portions, one of said end portions being secured in fixed position relative to said pump chamber defining means, the other of said end portions being attached to said pump piston, said end portions being movable generally toward and away from each other in response to variation of pneumatic fluid pressure in said pneumatic chamber, said actuator being operable to move said pump piston in one direction to reduce the volume of said pump chamber, and means for controlling the operation of said actuator.
 2. A spray coating apparatus as set forth in claim 1 wherein said shell has a surface of substantially constant area in each of the positions of said actuator, said shell in said axially extended position of said actuator has a fluted configuration defined by a circumaxially spaced series of axially extending ridges and valleys, and said shell in said axially retracted position of said actuator has a generally prolate spheroidal configuration.
 3. A spray coating apparatus as set forth in claim 2 wherein said shell is made from elastomeric material reinforced with other material to prevent change in the surface area thereof.
 4. A spray coating apparatus as set forth in claim 1 wherein said pump piston is movable in said one direction in response to movement of said actuator from its axially extended toward its axially contracted position.
 5. A spray coating apparatus as set forth in claim 1 wherein said apparatus includes means for operating said nozzle valve in timed relation to the operation of said actuator.
 6. A spray coating apparatus as set forth in claim 5 wherein said means for controlling the operation of said actuator comprises said means for operating said nozzle valve in timed relation to the operation of said actuator.
 7. A spray coating apparatus as set forth in claim 6 wherein said nozzle assembly includes means for biasing said nozzle valve to its closed position and pneumatically actuated means for moving said nozzle valve to its open position.
 8. A spray coating apparatus as set forth in claim 1 wherein said means for controlling the operation of said actuator comprises a pneumatic pressure fluid control circuit including a fluid pressure accumulator for connection to a source of pneumatic pressure fluid for receiving and containing a charge of pneumatic pressure fluid sufficient to effect operation of said actuator and control valve means for controlling the flow of pressure fluid from the source into said accumulator and for controlling the flow of pressure fluid from said accumulator into said actuator to effect operation thereof.
 9. A spray coating apparatus comprising a pump assembly including means defining a pump chamber and a pump piston supported in said chamber for movement in one and an opposite direction therein to vary the volume of said pump chamber, a nozzle assembly including a nozzle defining a point of emission for a stream of coherent fluent material, a nozzle valve movable between open and closed positions relative to said nozzle, means for biasing said nozzle valve to its closed position, and pneumatically actuated means for moving said nozzle valve to its open position, said nozzle valve in said open position permitting discharge of fluent material from said point of emission and in said closed position preventing discharge of material therefrom, means defining an inlet passageway communicating with said pump assembly for connection to a source of fluent material to provide a material flow path from the source to said pump chamber, a check valve associated with said inlet passageway for permitting material to flow from the source to said pump chamber and preventing retrograde flow of material from said pump cHamber to the source, means defining an outlet passageway communicating with said pump assembly and said nozzle assembly for providing a material flow path from said pump chamber to said point of emission, a pneumatic fluid pressure responsive actuator operably connected to said pump piston for moving it in one direction to reduce the volume of said pump chamber, and means for controlling the operation of said actuator and for operating said nozzle valve in timed relation to the operation of said actuator.
 10. A spray coating apparatus as set forth in claim 9 wherein said actuator comprises a hollow flexible thin-walled shell defining a pneumatic chamber of variable volume and having generally axially opposed end portions, said end portions being movable generally toward and away from each other between axially contracted and axially extended positions in response to variation of pneumatic fluid pressure in said chamber, one of said end portions being secured in fixed position relative to said pump chamber defining means, the other of said end portions being attached to said pump piston.
 11. A spray coating apparatus as set forth in claim 10 wherein said shell has a surface of substantially constant area in each of the positions of said actuator, said shell in said axially extended position of said actuator has a fluted configuration defined by a circumaxially spaced series of axially extending ridges and valleys, and said shell in said axially retracted position of said actuator has a generally prolate spheroidal configuration.
 12. A spray coating apparatus as set forth in claim 9 wherein said means for controlling the operation of said actuator comprises a pneumatic control circuit which includes a pilot valve for connection to a source of pneumatic pressure fluid and movable between open and closed positions, a pneumatically operated control valve means for controlling the operation of said actuator, means defining a first pneumatic fluid passageway communicating with said pilot valve and said control valve means, means defining a second pneumatic fluid passageway communicating with said pilot valve and said pneumatically actuated means for moving said nozzle valve, and means for operating said pilot valve to simultaneously connect said first and second pneumatic fluid passageways to the pneumatic pressure fluid supply source.
 13. A spray coating apparatus as set forth in claim 12 wherein said second pneumatic fluid passageway is substantially longer than said first pneumatic fluid passageway and comprises said means for operating said nozzle valve in timed relation to the operation of said actuator.
 14. A spray coating apparatus as set forth in claim 13 wherein said means for operating said pilot valve comprises a solenoid and said apparatus includes an adjustable timer for operating said solenoid to control the operating cycle of said apparatus.
 15. A spray coating apparatus comprising a pump assembly including means defining a pump chamber and a pump piston supported in said chamber for movement in one and an opposite direction therein to vary the volume of said pump chamber, a nozzle assembly including a nozzle defining a point of emission for a stream of coherent fluent material, a nozzle valve movable between open and closed positions relative to said nozzle, said nozzle valve in said open position permitting discharge of fluent material from said point of emission and in said closed position preventing discharge of material therefrom, means defining an inlet passageway communicating with said pump assembly for connection to a source of fluent material to provide a material flow path from the source to said pump chamber, a check valve associated with said inlet passageway for permitting material to flow from the source to said pump chamber and preventing retrograde flow of material from said pump chamber to the source, means defining an outlet passageway communicating with said pump assembly and said nozzle assembly for providing a material flow paTh from said pump chamber to said point of emission, a pneumatic fluid pressure responsive actuator operably connected to said pump piston for moving it in one direction to reduce the volume of said pump chamber, and a pneumatic pressure fluid control circuit for controlling the operation of said actuator and including a fluid pressure accumulator for connection to a source of pneumatic pressure fluid for receiving and containing a charge of pneumatic pressure fluid sufficient to effect operation of said actuator and control valve means for controlling the flow of pressure fluid from the source into said accumulator and for controlling the flow of pressure fluid from said accumulator into said actuator to effect operation thereof.
 16. A spray coating apparatus as set forth in claim 15 wherein said actuator comprises a hollow flexible thin-walled shell defining a pneumatic chamber of variable volume and having generally axially opposed end portions, said end portions being movable generally toward and away from each other between axially contracted and axially extended positions in response to variation of pneumatic fluid pressure in said chamber, one of said end portions being secured in fixed position relative to said pump chamber defining means, the other of said end portions being attached to said pump piston.
 17. A spray coating apparatus as set forth in claim 16 wherein said shell has a surface of substantially constant area in each of the positions of said actuator, said shell in said axially extended position of said actuator has a fluted configuration defined by a circumaxially spaced series of axially extending ridges and valleys, and said shell in said axially retracted position of said actuator has a generally prolate spheroidal configuration.
 18. A spray coating apparatus as set forth in claim 15 wherein said fluid control circuit includes a pilot valve for operating said control valve means and means for operating said pilot valve.
 19. A spray coating apparatus as set forth in claim 18 wherein said means for operating said pilot valve comprises an adjustable cycle timer.
 20. A spray apparatus as set forth in claim 18 wherein said control valve means comprises a normal open first accumulator valve for controlling the flow of pressure fluid from the source into said accumulator and a normally closed second accumulator valve for controlling the flow of pressure fluid from said accumulator into said actuator, said first and second accumulator valves being operable substantially simultaneously in response to operation of said pilot valve to prevent flow of pressure fluid from the source into said accumulator and to permit flow of pressure fluid from said accumulator into said actuator. 